The present invention relates to a load-applying device that includes a tensioner used to keep constant the tension of a belt or chain.
The tensioner, as one type of load-applying device, presses, for example, a timing chain or timing belt that is used in a car engine, with a predetermined force, and if the timing chain or timing belt elongates or slackens, the tensioner acts to keep the tension constant.
FIG. 31 shows the inside of an engine main body 200 of a car. Inside the engine main body 200 are arranged (1) a pair of cam sprockets 210, 210 that are driven shafts, and (2) a crank sprocket 220 that is a driving shaft. A timing chain 230 is stretched over the sprockets 210, 220 in an endless manner. The rotation of the crank sprocket 220 causes the timing chain 230 to move (travel) around the outer peripheries of the sprockets 210, 210, 220. A chain guide 240 is disposed along the moving route of the timing chain 230 so as to contact the timing chain 230, so that the timing chain 230 moves while sliding on the chain guide 240. The chain guide 240 is able to oscillate on a support shaft 250 so as to adjust the tension of the timing chain 230.
The reference sign 300 designates a tensioner that is provided inside the engine main body 200 and that is configured to press the chain guide 240 towards the timing chain 230. The tensioner 300 that is generally used has a configuration such that the tensioner expands and contracts in its axial direction to press the chain guide 240. This tensioner 300 includes a case 310 that is fixed to the inside of the engine main body 200, and a propulsion shaft 320 that is arranged inside the case 310 so as to be movable forward and backward. The propulsion shaft 320 is biased by a coil spring (not shown) that is arranged in the case 310 in such a manner as to move out from the case 310. The propulsion shaft 320 presses the chain guide 240 at distal end of the propulsion shaft 320 so as to provide tension to the timing chain 230.
The tensioner 300 shown in FIG. 31 is configured such that the coil spring and the propulsion shaft 320 are arranged inside the case 310, and such that the propulsion shaft 320 moves axially in both directions. As a result, the tensioner 300 becomes longer in the axial direction, limiting the extent to which the length of the tensioner 300 can be shortened in the axial direction, and therefore the tensioner 300 has a problem that it is not easily applied in a small engine. Accordingly, in order to overcome such a problem, a tensioner using a spiral spring has been developed. (See Patent Documents 1 and 2.)
The tensioner of Patent Document 1 includes a cam member made of an eccentric cam that oscillates a chain guide in the timing-chain-tension direction, and a spiral spring that biases the cam member to move in the direction to press the chain guide. A backstop claw engages with the cam member, which prevents the reverse movement of the cam member. The spiral spring has a configuration such that the inner end thereof is locked to the fixing pin of the engine main body, and the outer end thereof is locked to the cam member, so that the spiral spring, by the expansion of its diameter, biases the cam member to move and to press the chain guide.
The tensioner of Patent Document 2 also uses a spiral spring and a cam member, the cam member including a cam surface that is curved involutely. Also, a chain guide is coupled to a rolling bearing that rollably contacts the cam member's surface. Thus, the movement of the cam member causes the rolling bearing to roll on the surface of the cam. The spiral spring is configured such that the outer end thereof is locked to the engine main body, and the inner end thereof is locked to the cam member, so that the spiral spring biases the cam member to rotate, whereby the cam member is moved so as to press the chain guide.
The tensioners that are described in Patent Documents 1 and 2, respectively, are configured such that a cam member coupled to a spiral spring contacts a chain guide to provide tension to a timing chain by causing it to oscillate, which eliminates the reciprocal axial movement of the tensioner, which allows the axial length of the tensioner to be shortened.